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Leveraging Locality of Reference for Certificate Revocation
X.509 certificate revocation defends against man-in-the-middle attacks involving a compromised certificate. Certificate revocation strategies face scalability, effectiveness, and deployment challenges as HTTPS adoption rates have soared. We propose Certificate Revocation Table (CRT), a new revocation strategy that is competitive with or exceeds alternative state-of-the-art solutions in effectiveness, efficiency, certificate growth scalability, mass revocation event scalability, revocation timeliness, privacy, and deployment requirements. The CRT design assumes that locality of reference applies to the certificates accessed by an organization. The CRT periodically checks the revocation status of X.509 certificates recently used by the organization. Pre-checking the revocation status of certificates the clients are likely to use avoids the security problems of on-demand certificate revocation checking.
To validate both the effectiveness and efficiency of our approach, we simulated a CRT using 60 days of TLS traffic logs from Brigham Young University to measure the effects of actively refreshing revocation status information for various certificate working set window lengths. A working set window size of 45 days resulted in an average of 99.86\% of the TLS handshakes having revocation information cached in advance. The CRT storage requirements are small. The initial revocation status information requires downloading a 6.7 MB file, and subsequent updates require only 205.1 KB of bandwidth daily. Updates that include only revoked certificates require just 215 bytes of bandwidth per day.